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Overcoming the ‘CO2 penalty’ of autonomous vehicles

2017-04-03
Lindsay Brooke

What type of propulsion system will power the highly automated (SAE Level 4) and fully autonomous (SAE Level 5) vehicles of the future? Such systems will need to be more efficient than those used in today’s human-driven vehicles, to offset the “autonomous overhead”—the significant amount of electrical power required for data processing alone. And they won’t be the lowest-cost solution, according to Chris Thomas, BorgWarner’s vice president and CTO.

The 1.5 kW to 2.75 kW needed just to process the increasing deluge of incoming and in-vehicle data—generated from on-board sensor arrays, from other vehicles, the infrastructure and the cloud—is “the dirty little secret” of autonomous vehicle engineering, Thomas told the audience at SAE’s 2017 High-Efficiency Engines Symposium in Detroit on April 3.

For a typical B-segment vehicle, for example, about 39 W of electricity consumed is equivalent to about one gram of CO2 emitted.

Thomas noted that new dedicated processors from Intel and Nvidia will inevitably help reduce electrical consumption by up to 90%. That means that with a 90% reduction in energy consumption, a typical vehicle’s processing power demand may be 200 to 350 W.

“By our calculations, the best case-scenario is that we’ll end up with about a 10-g to 20-g CO2 penalty per autonomous vehicle,” Thomas explained, translating into a 3-6% burden for the propulsion system and a significant “hit” to vehicle efficiency.

“That means the propulsion system has to be that much better than today’s,” he noted. “We need to get to a 50-51% BTE to make that happen. That’s not plausible without hybridization coupled with significantly more efficient combustion engines.”

While Thomas considers autonomous vehicles to be “propulsion agnostic,” the need for redundant braking systems (and redundant batteries) makes plug-in hybrids the practical prime-mover in this area for perhaps the next 20 years. He reckons battery-electric vehicles won’t play a major role in autonomous use during that period.

“The increased uptime of autonomous vehicles could mean more than 10 hours per day of operation, in which a significant amount of charging would be required,” he argues. “A typical New York cab runs 18 hours a day which means it needs 18 hours of air conditioning in the summer and 18 hours of heat in winter. In a BEV you lose 30-50% of the range when you turn the A/C or heat on. So I don’t think we’ll see BEVs used for autonomy outside of some commercial vehicles, at least in the short term.”

If battery exchanges/swapping at centralized locations were made accessible, that scenario could change if an infrastructure (similar to gas stations) were implemented, he said. DC fast charging of entire fleets of vehicles would create too great a spike in the electrical grid to be practical, Thomas noted.